1. Field of the Invention
The present invention relates to a pipe joint made of resin which is preferably used in piping for a liquid having high purity or ultrapure water to be handled in a production process in, for example, the production of semiconductor devices, the production of medical equipment and medicines, for food processing, and in the chemical industry.
2. Description of the Prior Art
Conventionally, as pipe joints made of resin of this kind, those having a configuration like that shown in FIGS. 4 to 6 are known. Among them, the pipe joint made of resin shown in FIG. 4 (see Japanese Utility Model Publication No. 7-20471) comprises a joint body 1, a sleeve 2, and a union nut 3 which are made of resin. In the joint body 1, a pipe receiving port 5 is formed at one end in the axial direction. A first sealing portion 6 is formed in an inner area of the pipe receiving port 5, and a second sealing portion 7 is formed in an entrance area of the pipe receiving port 5 so that the sealing portions intersect the axis C of the joint body 1. An external thread portion 9 is formed on the outer periphery of the pipe receiving port 5. In the sleeve 2, a fitting portion 10 having an outer diameter that allows the portion to be fitted into the receiving port 5 of the joint body 1 is formed in an inner end portion in the axial direction, and a bulge portion 15 having a mountain-like section shape is formed in an outer end side in the axial direction. The sleeve 2 is pressingly inserted into one end portion 17 of a tube 11 made of resin under a state where the fining portion 10 projects outwardly. As a result of this press insertion, the diameter of the one end portion 17 of the tube 11 is increased. An inner end sealing portion 13 which abuts against the sealing portion 6 of the joint body 1 is formed in an end portion of the fitting portion 10, and an outer peripheral sealing face 18 which abuts against the sealing portion 7 of the pipe receiving port 5 is formed in a place corresponding to the bulge portion 15. In the union nut 3, an internal thread portion 20 which is to be screwed to the external thread portion 9 of the joint body 1 is formed.
The one end portion 17 of the tube 11 into which the sleeve 2 is pressingly inserted is inserted into the receiving port 5 of the joint body 1. Under this state, the internal thread portion 20 of the union nut 3 which is previously loosely fitted onto the outer periphery of the one end portion 17 of the tube 11 is screw-fastened to the external thread portion 9 of the joint body 1. This fastening causes the sleeve 2 to be pressed in the axial direction, so that the inner end sealing portion 13 and the outer peripheral sealing face 18 of the sleeve 2 abut against the sealing portions 6 and 7 of the pipe receiving port 5 of the joint body 1, respectively, thereby exerting a sealing function.
In the pipe joint made of resin shown in FIG. 5, a tapered sealing portion 30 in which the diameter is gradually reduced toward the inner side in the axial direction is formed in an entrance area of a receiving port 5 of a joint body 1 into which the one end portion 17 of the tube 11 made of resin is to be inserted, and a sealing portion 31 which abuts against a tapered sealing portion 30 is formed in the inner end of a sleeve 2. The sleeve 2 is fitted onto the one end portion 17 of the tube 11, whereby a bulge portion 32 which is locally projected toward the radially inner side is formed on the one end portion 17 of the tube 11. The internal thread portion 20 of the union nut 3 which is previously loosely fitted onto the outer periphery of the one end portion 17 of the tube 11 is fastened to an external thread portion 9 of the joint body 1. This fastening causes the sleeve 2 to be pressed in the axial direction, so that sealing portions 30 and 31 abut against each other, thereby exerting a sealing function.
In the pipe joint made of resin shown in FIG. 6, a tapered sealing portion 33 in which the diameter is gradually reduced toward the inner side in the axial direction is formed in an entrance area of a receiving port 5 of a joint body 1 into which the one end portion 17 of the tube 11 made of resin is to be inserted. A sleeve 2 which has an outer peripheral wall 34 having a trapezoidal section shape is pressingly inserted into the inner periphery of the one end portion 17 of the tube 11. As a result of this press insertion, a bulge portion 35 which is locally projected toward the radially outer side along the outer peripheral wall 34 of the sleeve 2 is formed on the tube 11. The internal thread portion 20 of the union nut 3 which is previously loosely fitted onto the outer periphery of the one end portion 17 of the tube 11 is fastened to an external thread portion 9 of the joint body 1, whereby the bulge portion 35 of the tube 11 and the sleeve 2 are pressed against the joint body 1 and an inclined face 36 on the tube end side of the bulge portion 35 is pressed against the tapered sealing portion 33 in the axial direction, so as to exert a sealing force.
As described above, all of the conventional pipe joints made of resin shown in FIGS. 4 to 6 comprise: the joint body 1 which is made of resin, and which has the pipe receiving port 5 in one end portion, and the external thread portion 9 on the outer periphery of the pipe receiving port 5; the sleeve 2 which is made of resin, and which is to be pressingly inserted into the inner or outer periphery of the one end portion 17 of the tube 11 made of resin to be integrated therewith; and the union nut 3 which is made of resin, which is loosely fitted onto the outer periphery of the one end portion 17 of the tube 11, and which is screwed via the internal thread portion 20 to the external thread portion 9 of the joint body 1. The one end portion 17 of the tube 11 into which the sleeve 2 is pressingly inserted to be integrated therewith is inserted into the pipe receiving port 5 of the joint body 1. The gap between the one end portion 17 of the tube 11 and the pipe receiving port 5 of the joint body 1 is sealed in a water blocking manner via the sleeve 2 which is pressed against the joint body 1 by fastening the union nut 3.
In all of the conventional pipe joints made of resin, the external thread portion 9 of the joint body 1 and the internal thread portion 20 of the union nut 3 use triangular threads according to usual thread standards. Such triangular threads have an included angle of 55° or 60° (see FIG. 4).
However, usual thread standards are originally introduced for metals, and, in some cases, are not suitable to threads for resin such as those for a pipe joint made of resin because, when a pipe joint is made of resin, creep deformation which advances over time under a constant load is largely affected by the load and the temperature.
In the pipe joint made of resin in which the sleeve 2 and the joint body 1 are pressed against each other by fastening the union nut 3, a creep phenomenon and stress relaxation due to the phenomenon occur in a portion where the sleeve 2 and the joint body 1 are pressed, thereby causing the liquid to leak or the tube 11 to slip off. Therefore, functions which are exerted by pressing the two components, i.e., the sleeve 2 and the joint body 1, such as the sealing function, and the function of preventing the tube 11 from slipping off must be ensured. Therefore, it is required to set a pressing force which is necessary and sufficient for exerting functions such as the sealing function. In the case where a creep phenomenon or the like occurs and the union nut 3 is to be further fastened, adjustment of the pressing force must be performed at a higher degree.
As the resin material of a pipe joint of this kind, fluororesin which has excellent heat resistance and chemical resistance is usually used. When triangular threads according to usual metal thread standards are applied to the internal thread portion 20 of the union nut 3 and the external thread portion 9 of the joint body 1 which are made of such fluororesin, it is sometimes difficult to obtain a desired pressing force in the axial direction corresponding to the fastening torque of the union nut 3 under severe and extreme use conditions which are much severer than usual use conditions, such as those in which the temperature of a fluid to be transported is higher than 200° C., or the pressure of the fluid is higher than 1 MPa. Even when the internal and external thread portions 20 and 9 are not broken, there arises a case where the sealing property and the resistance to tube slipping off which are required in a pipe joint are not sufficiently satisfied. Specifically, a remarkable creep phenomenon of the resin material may cause a case where the force (fastening torque) of rotating the union nut 3 in the fastening direction exceeds the strength of the threads and the threads are broken, or that where the internal thread portion 20 of the union nut 3 slips over threads of the external thread portion 9 of the joint body 1, and the union nut 3 swells toward the radially outer side, so that the internal thread portion 20 is disengaged from the external thread portion 9 and the union nut is freely rotated.